The invention relates to a device for generating X-rays, which device comprises a source for emitting electrons, a liquid metal for emitting X-rays as a result of the incidence of electrons, and a displacing member for displacing the liquid metal through an impingement position where the electrons emitted by the source impinge upon the liquid metal.
A known device for generating X-rays is described in U.S. Pat. No. 6,185,277-B1. During operation of the known device, the liquid metal, e.g. mercury, flows through a narrow passage which forms part of a closed cyclical channel system. Said narrow passage is bounded by a relatively thin window made from a material which is transparent to X-rays and electrons, e.g. diamond. The window separates the liquid metal from a vacuum space in which the source is accommodated. The source generates an electron beam, which passes through the window and impinges upon the liquid metal in the impingement position behind the window. The X-rays, emitted by the liquid metal as a result of the incidence of the electron beam, emanate through the window and through an X-ray exit window, which is provided in a housing surrounding the vacuum space. The velocity of the liquid metal flow in the narrow passage is relatively high, so that the flow in this passage is highly turbulent. As a result of this turbulent flow, the heat, which is generated in the impingement position as a result of the incidence of the electron beam upon the liquid metal, is transported away from the impingement position in a considerably effective manner, so that an increase of the temperature of the liquid metal in the impingement position is limited. The channel system further comprises a heat exchanger by means of which the liquid metal is cooled down. The displacing member, by means of which the liquid metal is displaced through the narrow passage, the heat exchanger, and the other parts of the channel system, is a pump which is arranged in the channel system between the heat exchanger and the narrow passage.
A disadvantage of the known device for generating X-rays is that the pump has to generate a relatively high pressure of the liquid metal in order to obtain flow velocities in the narrow passage which are sufficiently high to obtain a sufficient rate of heat transport away from the impingement position by the liquid metal flow. This is the result of relatively high pressure losses of the liquid metal flow in the narrow passage. As a result, a relatively heavy and robust pump has to be used, and also other parts of the device, which are exposed to the high pressure, have to be constructed in a robust manner. This causes the known device to be less suitable for use in systems where a large weight and large dimensions of the device are not practical or even intolerable, which is particularly the case in medical X-ray examination systems. Furthermore, the relatively thin X-ray and electron transparent window may easily break as a result of the high pressure, causing malfunction of the device.